This invention relates to the improvement of an apparatus useful for continuously measuring the electrical charge condition of electrically nonconductive, but electrically charged, particles suspended in a supporting liquid such as water. For example, this apparatus can continuously measure the charge concentration of the silt suspended in river water, used in industrial processes or the charge concentration of particles suspended in sewage.
Usually it is desirable to remove such suspended particles before using them in industrial processes. This is often accomplished by adding flocculating agents of opposite electric charge. The flocs thus formed are then readily removed by such methods as sedimentation, filtration, flotation, centrifugation and the like. One problem, of course, in adding such flocculating agents, is knowing which type of charged agent to add, that is negatively or positively charged agents. A second problem is to know how much of such agent should be added. Adding too little does not result in the maximum flocculation and suspended particle removal. On the other hand adding too much flocculating agent can result in shifting the electrical imbalance too far which may contribute to the suspension stability thus having an undesirable effect. Thus in streams such as river water flowing continuously into industrial plants wherein it is highly desirable to remove the suspended solids therefrom, it is highly desirable to be able to measure accurately the charge concentration of the non-conductive suspended particles even though the concentration varies so that the exact amount of the correctly charged flocculating agent can be added to the stream.
A partially successful attempt at making an apparatus which sould make such continuous measurements is disclosed in W. F. Gerdes U.S. Pat. No. 3,368,145, issued on Feb. 6, 1968, and incorporated herein by reference. This prior art apparatus, for which the present invention is an improvement, measures this particle charge conditions by measuring the streaming current (electrical) of the liquid suspension as it is swiftly forced past two spaced electrodes located in a substantially vertical, but inverted, piston and cylinder configuration. In this configuration both the interior of the cylinder wall and the external wall of the piston are electrically non-conductive, the cylinder is closed at its bottom and open at its top to allow entry and exit of the suspension sample being measured. The piston is fitted loosely enough within the cylinder so that when it is reciprocated within the cylinder the suspension sample is forced in and out of the cylinder between the walls of the piston and cylinder at a sufficiently fast velocity and under a sufficient pressure to ideally measure the streaming current of the suspension sample, and hence give an alternating electrical signal at the two electrodes which is a function of the charge concentration on the suspended particles within the sample. However, considerable difficulty has been met by trying to use this apparatus under field conditions. Erratic and erroneous measurements are often encountered after only a few hours field service.
It would be highly advantageous to eliminate these measurement errors and provide an apparatus which was accurate and stable over a long period of time in both the field and the lab. The present invention achieves this and other advantages.